Such electronic motion picture cameras (also referred to as video cameras) can generate and record digital motion picture sequences and/or can transfer them to an external recording apparatus. To set and monitor the image section and/or camera parameters such as focus, focal length and exposure, an output of the generated images can take place at a display device, e.g. at an electronic viewfinder integrated into the motion picture camera and/or at an external viewfinder or monitor. The frame rate of the motion picture camera at which the image sensor is operated (i.e. at which the image information is detected and read out of the image sensor) can be freely selected within certain limits. The frame rate is also called the frame frequency. A frame rate of 24 frames per second (fps) is frequently selected to adapt the perceived impression presented to a viewer to that of motion picture movies produced with conventional moving picture cameras. With such analog moving picture cameras, a frame rate of 24 fps is typically preset, with the exposure time corresponding to half a frame period.
A display of the images taken by an electronic motion picture camera at a viewfinder or monitor at the same display rate, i.e. likewise 24 fps, can result in perceptible image flicker. A display of the taken images at a substantially higher display rate, for example approximately 100 fps, is therefore targeted.
As a rule, electronic motion picture cameras therefore have at least one buffer memory into which the respective images taken by the image sensor are written. The respective current image is periodically read from the buffer memory in accordance with the display rate of the display device and is displayed at the display device. Since in the named example, the display rate is higher than the frame rate, the reading out and displaying of a respective image stored in the buffer memory is therefore repeated several times before the next stored image is read out and displayed.
Different refresh rates in the presentation can arise with different images depending on the relationship between the frame rate and the display rate. With the above-named rates, the images are sometimes displayed at the display device four times after one another; occasionally, however, even five times after one another. A fivefold display takes place when no new image is yet available for display in the buffer memory after the end of the fourth display of an image. The resulting different display durations of the individual frames, i.e. the different display durations perceived by a viewer of the display device, can result in a jerky and less smooth perception. In addition, due to a constantly varying phasing between the image capture and the image display, an undesirably high delay can result between the taking of an image and the display of this image at the display device (so-called latency time). The camera work (e.g. punctual pan shot) is hereby made more difficult. This is in particular the case in the aforesaid example when the previously taken image still stored in the buffer memory is already being displayed a fifth time—briefly before a new image has been taken by the image sensor and is written to the buffer memory.